Blazing fast, Zap-based Stackdriver logging.

This package provides three building blocks to support the full array of structured logging capabilities of Stackdriver:

• Special purpose logging fields
• Pre-configured Stackdriver-optimized encoder
• Custom Stackdriver Zap core
• Using Error Reporting

The above components can be used separately, but to start, you can create a new Zap logger with all of the above included:

logger, err := zapdriver.NewProduction() // with sampling
logger, err := zapdriver.NewDevelopment() // with `development` set to `true`

The above functions give back a pointer to a zap.Logger object, so you can use Zap like you've always done, except that it now logs in the proper Stackdriver format.

You can also create a configuration struct, and build your logger from there:

config := zapdriver.NewProductionConfig()
config := zapdriver.NewDevelopmentConfig()

Or, get the Zapdriver encoder, and build your own configuration struct from that:

encoder := zapdriver.NewProductionEncoderConfig()
encoder := zapdriver.NewDevelopmentEncoderConfig()

Read on to learn more about the available Stackdriver-specific log fields, and how to use the above-mentioned components.

You can use the following fields to add extra information to your log entries. These fields are parsed by Stackdriver to make it easier to query your logs or to use the log details in the Stackdriver monitoring interface.

• HTTP
• Label
• SourceLocation
• Operation
• TraceContext

You can log HTTP request/response cycles using the following field:

HTTP(req *HTTPPayload) zap.Field

You can either manually build the request payload:

req := &HTTPPayload{
  RequestMethod: "GET",
  RequestURL: "/",
  Status: 200,
}

Or, you can auto generate the struct, based on the available request and response objects:

NewHTTP(req *http.Request, res *http.Response) *HTTPPayload

You are free to pass in nil for either the request or response object, if one of them is unavailable to you at the point of logging. Any field depending on one or the other will be omitted if nil is passed in.

Note that there are some fields that are not populated by either the request or response object, and need to be set manually:

• ServerIP string
• Latency string
• CacheLookup bool
• CacheHit bool
• CacheValidatedWithOriginServer bool
• CacheFillBytes string

If you have no need for those fields, the quickest way to get started is like so:

logger.Info("Request Received.", zapdriver.HTTP(zapdriver.NewHTTP(req, res)))

You can add a "label" to your payload as follows:

Label(key, value string) zap.Field

Note that underwater, this sets the key to labels.<key>. You need to be using the zapdriver.Core core for this to be converted to the proper format for Stackdriver to recognize the labels.

See "Custom Stackdriver Zap core" for more details.

If you have a reason not to use the provided Core, you can still wrap labels in the right labels namespace by using the available function:

Labels(fields ...zap.Field) zap.Field

Like so:

logger.Info(
  "Did something.",
  zapdriver.Labels(
    zapdriver.Label("hello", "world"),
    zapdriver.Label("hi", "universe"),
  ),
)

Again, wrapping the Label calls in Labels is not required if you use the supplied Zap Core.

You can add a source code location to your log lines to be picked up by Stackdriver.

Note that you can set this manually, or use zapdriver.Core to automatically add this. If you set it manually, and use zapdriver.Core, the manual call stack will be preserved over the automated one.

SourceLocation(pc uintptr, file string, line int, ok bool) zap.Field

Note that the function signature equals that of the return values of runtime.Caller(). This allows you to catch the stack frame at one location, while logging it at a different location, like so:

pc, file, line, ok := runtime.Caller(0)

// do other stuff...

logger.Error("Something happened!", zapdriver.SourceLocation(pc, file, line, ok))

If you use zapdriver.Core, the above use-case is the only use-case where you would want to manually set the source location. In all other situations, you can simply omit this field, and it will be added automatically, using the stack frame at the location where the log line is triggered.

If you don't use zapdriver.Core, and still want to add the source location at the frame of the triggered log line, you'd do it like this:

logger.Error("Something happened!", zapdriver.SourceLocation(runtime.Caller(0)))

The Operation log field allows you to group log lines into a single "operation" performed by the application:

Operation(id, producer string, first, last bool) zap.Field

For a pair of logs that belong to the same operation, you should use the same id between them. The producer is an arbitrary identifier that should be globally unique amongst all the logs of all your applications (meaning it should probably be the unique name of the current application). You should set first to true for the first log in the operation, and last to true for the final log of the operation.

logger.Info("Started.", zapdriver.Operation("3g4d3g", "my-app", true, false))
logger.Debug("Progressing.", zapdriver.Operation("3g4d3g", "my-app", false, false))
logger.Info("Done.", zapdriver.Operation("3g4d3g", "my-app", false, true))

Instead of defining the "start" and "end" booleans, you can also use these three convenience functions:

OperationStart(id, producer string) zap.Field
OperationCont(id, producer string) zap.Field
OperationEnd(id, producer string) zap.Field

You can add trace context information to your log lines to be picked up by Stackdriver.

TraceContext(trace string, spanId string, sampled bool, projectName string) []zap.Field

Like so:

logger.Error("Something happened!", zapdriver.TraceContext("105445aa7843bc8bf206b120001000", "0", true, "my-project-name")...)

The Stackdriver encoder maps all Zap log levels to the appropriate Stackdriver-supported levels:

DEBUG (100) Debug or trace information.

INFO (200) Routine information, such as ongoing status or performance.

WARNING (400) Warning events might cause problems.

ERROR (500) Error events are likely to cause problems.

CRITICAL (600) Critical events cause more severe problems or outages.

ALERT (700) A person must take an action immediately.

EMERGENCY (800) One or more systems are unusable.

It also sets some of the default keys to use the right names, such as timestamp, severity, and message.

You can use this encoder if you want to build your Zap logger configuration manually:

zapdriver.NewProductionEncoderConfig()

For parity-sake, there's also zapdriver.NewDevelopmentEncoderConfig(), but it returns the exact same encoder right now.

A custom Zap core is included in this package to support some special use-cases.

First of all, if you use zapdriver.NewProduction() (or NewDevelopment) , you already have this core enabled, so everything just works ™.

There are two use-cases which require this core:

1. If you use zapdriver.Label("hello", "world"), it will initially end up in your log with the key labels.hello and value world. Now if you have two labels, you could also have labels.hi with value universe. This works as- is, but for this to be correctly parsed by Stackdriver as true "labels", you need to use the Zapdriver core, so that both of these fields get rewritten, to use the namespace labels, and use the keys hello and hi within that namespace. This is done automatically.

2. If you don't want to use zapdriver.SourceLocation() on every log call, you can use this core for the source location to be automatically added to each log entry.

When building a logger, you can inject the Zapdriver core as follows:

config := &zap.Config{}
logger, err := config.Build(zapdriver.WrapCore())

To report errors using StackDriver's Error Reporting tool, a log line needs to follow a separate log format described in the Error Reporting documentation.

The simplest way to do this is by using NewProductionWithCore:

logger, err := zapdriver.NewProductionWithCore(zapdriver.WrapCore(
  zapdriver.ReportAllErrors(true),
  zapdriver.ServiceName("my service"),
))

For parity-sake, there's also zapdriver.NewDevelopmentWithCore()

If you are building a custom logger, you can use WrapCore() to configure the driver core:

config := &zap.Config{}
logger, err := config.Build(zapdriver.WrapCore(
  zapdriver.ReportAllErrors(true),
  zapdriver.ServiceName("my service"),
))

Configuring this way, every error log entry will be reported to Stackdriver's Error Reporting tool.

If you do not want every error to be reported, you can attach ErrorReport() to log call manually:

logger.Error("An error to be reported!", zapdriver.ErrorReport(runtime.Caller(0)))
// Or get Caller details
pc, file, line, ok := runtime.Caller(0)
// do other stuff... and log elsewhere
logger.Error("Another error to be reported!", zapdriver.ErrorReport(pc, file, line, ok))

Please keep in mind that ErrorReport needs a ServiceContext attached to the log entry. If you did not configure this using WrapCore, error reports will get attached using service name as unknown. To prevent this from happeneing, either configure your core or attach service context before (or when) using the logger:

logger.Error(
  "An error to be reported!",
  zapdriver.ErrorReport(runtime.Caller(0)),
  zapdriver.ServiceContext("my service"),
)

// Or permanently attach it to your logger
logger = logger.With(zapdriver.ServiceContext("my service"))
// and then use it
logger.Error("An error to be reported!", zapdriver.ErrorReport(runtime.Caller(0)))